SIGABRT under load (tracked to vm_map_find() returning KERN_NO_SPACE)

[Alan Cox]

Elsewhere, specifically kern_exec.c, we use kmem_alloc_wait() and
kmem_free_wakeup() to allocate and deallocate exec_map space.  These
functions allow for sleeping until virtual address space is
available.  Try mechanically converting the vm_map_find() and
vm_map_remove() calls in imgact_elf.c to kmem_alloc_wait() and
kmem_free_wakeup().

Alan